What is the greenhouse effect?

The statements that are $TRUE$:
$A$. Methane leads to both global warming and photochemical smog.
$B$. Methane is generated from paddy fields.
$C$. Methane is a stronger global warming gas than $CO_2$.
$D$. Methane is a part of reducing smog.
Choose the most appropriate answer from the options given below:

The regions of the atmosphere,where clouds form and where we live,respectively,are

The concentration of dissolved oxygen in water for the growth of fish should be more than $X \ ppm$ and the Biochemical Oxygen Demand $(BOD)$ in clean water should be less than $Y \ ppm$. $X$ and $Y$ in $ppm$ are,respectively:

Methyl mercaptans are generated as waste from which industry?

Which of the following practices will not come under green chemistry?
$1$. Using soaps made of vegetable oils instead of synthetic detergents,whenever possible.
$2$. Using $H_2O$ for bleaching purposes instead of chlorine-based bleaching agents.
$3$. Using liquefied $CO_2$ for dry cleaning clothes and laundry.
$4$. Using plastic cans for neatly storing substances.